Heat treatment of chromium-free steel bearings



United States Patent 3,155,550 HEAT TREATMENT (2F CHRQMHUM-FREE STEEL BEARINGS Joseph R. Mitchell, Chicago, Mary E. Potter, Thornton Township, Cook (Iounty, and Edmond .l. Whittenbcrger, Homewood, 111., assignors to United States Steel Corporation, a corporation of New Jersey No Drawing. Filed Sept. 15, 1961, Ser. No. 138,277 2 Claims. (61. 148-134) This application relates to steel bearings and their use.

Steel bearings are subject to heavy stresses at high temperatures. To attain satisfactory service under such condition, it has heretofore been regarded as essential that the bearings be formed of highly alloyed steels containing chromium which renders the steels quite expensive.

It is accordingly an object of this invention to provide economical, low cost steel bearings.

It is a further object to provide low alloy bearing steels which can be heat treated to produce a desirable microstructure for bearing use.

We have found that steel bearings attaining the foregoing objects can be produced from chromium-free hypereutectoid steels containing manganese, silicon and molybdenum within restricted ranges. The desired properties can be obtained within the following ranges:

.80 to 1.20% carbon .95 to 1.50 manganese .20 to .90 silicon .10 to .35 molybdenum .05 maximum aluminum with the balance iron and residual impurities.

' A preferred range within the foregoing is as follows:

.95 to 1.10% carbon 1.00 to 1.30 manganese .20 to .35 silicon .13 to .20 molybdenum .05 maximum aluminum with the balance iron and residual impurities.

Another preferred range is as follows:

.95 to 1.10% carbon 1.00 to 1.30 manganese .50 to .80 silicon .13 to .20 molybdenum .05 maximum aluminum with the balance iron and residual impurities.

The desired microstructure may be developed in such steels by the following heat treatments:

(1) Normalize by heating to within the range of 1550 and 1650 F. and air cooling (2) Spheroidize by a. Heating to between 1225 and 1275 F. and holding for 2 to 4 hours b. Raising temperature to 1375 to 1425 F. and hold in such range for 1 to 3 hours c. Furnace cooling to 1225 to 1275 F. and hold in such range for 1 to 3 hours at. Cooling at rate of 5 to F. per hour to below 1200 F. and air cooling (3) Transform by quenching from 1475 to 1575 F.

Specific examples of steels within the foregoing range are given below:

0 Mn S1 P l S Mo 3,155,550 Patented Nov. 3, 1964 Steel A contained 04% residual nickel and 03% residual chromium. Steel B contained residual nickel and chromium in the amount of 01% each.

These steels were deoxidized with aluminum at the rate of 2 pounds per ton and the ingots formed thereform were forged in the temperature range of 2100 to 1800" F. into rounds and slow cooled.

The forged steels were thereafter heat treated by the following steps to develop the desired microstructure and properties:

(1) Normalized by heating to 1600 F. and air cooled (2) Spheroidized by a. Heating to 1250" F. and holding for 3 hours b. Raising temperature to 1400 F. and holding for 1 hour 0. Furnace cooled to 1 250 F. and holding for 2 hours d. Cooled to 1180 F. at 10 F. per hour e. Air cooled to room temperature from 1180 F. (3) Transformed by a. Austenitizing in the range or" 1475 to 1575 F. 5. Water quenching Ideal diameter tests were made on these steels with the results shown in the following Table I:

The spheroidized specimens when quenched from 1525 and 1575 F. had ASTM grain size of 7 for Steel A and 6 for Steel B and have microstructures composed essentially of martensite with bainite as the first transformation product. Both have well distributed carbides pro viding bearings formed therefrom with good wear resistance.

It is accordingly seen that the hypereutectoid chromiumfree steels of this invention containing low amounts of manganese and molybdenum have such high hardenability that they will withstand stressing at temperatures above 300 F. for long periods and therefore are most suitable for bearing use.

While we have shown and described two specific embodiments of our invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, as defined in the appended claims.

We claim:

1. The method of producing steel suitable for bearings characterized by good wear resistance and stress resistance at temperatures above 300 F., comprising making chromium-free steel containing .80 to 1.20% carbon .95 to 1.50 manganese .20 to .90 silicon .10 to .35 molybdenum .05 maximum aluminum with the balance iron and residual impurities, spheroidizing said steel by heating it to between 1225 and 1275 F. and holding for 2 to 4 hours, raising the temperature thereof to 1375 to 1425 F. and holding for'l to 3 hours, reducing the temperature to between 1225 and 1275 F. and holding for 1 to 3 hours and cooling therefrom at a rate of 5 to 15 F. per hour to below 1200 F. and then transforming the steel to a microstructure composed essentially of martensite by heating it to between 1475 and 1575 F. and quenching.

2. The method of producing steel suitable for bearings characterized by good wear resistance and stress resistance at temperatures above 300 F., comprising making chromium-free steel containing .95 to 1.20% carbon 1.00 to 1.50 manganese .20 to .90 silicon .10 to .35 molybdenum .05 maximum aluminum with the balance iron and residual impurities, spheroidizing said steel by heating it to between 1225 and 1275 F. and holding for 2 to 4 hours, raising the temperature thereof to 1375 to 1425 F. and holding for 1 to 3 hours,

References Cited in the file of this patent UNITED STATES PATENTS 1,278,207 Potter Sept. 10, 1918 2,087,764 Bonte July 20, 1937 2,630,382 Wasserman Mar. 3, 1953 2,662,010 Ahles Dec. 8, 1953 OTHER REFERENCES A.S.M. Handbook (1948 edition), published by the A.S.M., pages 660662.

Heat Treatment of Metals, Brooker et al., published by the A.S.M., 1946, pages 4041 relied on.

km 7W UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,155,550 November 3', 1964 Joseph R. Mitchell et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 9, for '295" read .80 line 10, for "1.00" read .95

Signed and sealed this 30th day of March 1965,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J BRENNER Aitesting Officer Commissioner of Patents 

1. THE METHOD OF PRODUCING STEEL SUITABLE FOR BEARINGS CHARACTERIZED BY GOOD WEAR RESISTANCE AND STRESS RESISTANCE AT TEMPERATURES ABOVE 300*F., COMPRISING MAKING CHROMIUM-FREE STEEL CONTAINING 